Manifold reactors have reburning chambers for reburning the residual carbon monoxide and hydrocarbons in the exhaust gas. These constituents, when reburned, attain a high temperature in the range of 900.degree..about.1000.degree. C., so that it is necessary to heat-insulate the reburning chamber to prevent heat transfer to the engine casing as well as to enhance the gas purifying efficiency through efficient reburning.
In conventional methods of heat-insulating a manifold reactor the space between support casing and the outer shell supporting the inner shell is usually filled with a heat-insulating material. The heat-insulating material is so poor in its recuperative powers that, after exposure to repeated cycles of expansion and contraction due to temperature variations in the outer shell of the reburning chamber, the reburning chamber develops a gap between its outer shell and the heat-insulating material; and the heat-insulating material escapes through this gap due to the vibration produced during operation of the vehicle.
As a result the heat-insulation of the manifold reactor becomes less effective and the heat transfer to the engine casing increases, thereby causing various difficulties and unfavorable effects, such as a drop in the gas purifying efficiency.